Are the real estate and money that the father distributed among his sons and daughters before his death, from which he excluded one of his sons, considered an inheritance that must be divided or a valid gift?

The first advice is to pray for mercy and forgiveness for the father.

What the father bestowed upon his children during his lifetime and which they possessed before his death, becomes their private property, and other heirs do not share in it, even if it involved injustice. This is the view of the majority of jurists. If the father dies before reclaiming the gift, it remains valid for the donee. However, Sheikh al-Islam Ibn Taymiyyah preferred the permissibility of revoking an unjust gift even after death.

As for a gift made with the condition that it not be disposed of until after his death, this is not considered valid, because it is a bequest to an heir, and it does not nullify the right of the other heirs.